Research Reports and Memoranda

The first solution of the problem of finding the wall‐interference of a wind tunnel of elliptic cross‐section was given by Sanuki and Tani. The method used in that investigation does not give a physical picture of the phenomenon and does not appear to be very suitable for engineers, to handle. I. Lotz gave a general method for the correction of down‐wash in wind tunnels. Using Lotz's method of converting the elliptic boundary of the tunnel into two parallel planes by the use of elliptic co‐ordinates, Gavin and Hensel have worked out the upwash due to the walls of the M.I.T. Tunnel. This method has the advantage of representing the effect of the wall as equivalent to a system of images due to the tip vortices of the airfoil placed inside. However, in getting the value of the velocity induced by the image vortices, the series requires the values of these image positions in elliptic co‐ordinates. The method used in the present paper avoids the exponential functions, by using a different function for transforming the ellipse, and the image system is obtained by using simple algebraic functions only.